Tire vulcanizing molds are provided with vent mechanisms which discharge air left between a green tire and the mold and gas resulting from vulcanizing to the outside of the mold. Heretofore, various types of vent mechanisms which develop no spews have been proposed (see Patent Documents 1 and 2, for example).
Patent Document 1 proposes a vent mechanism using a laminated blade which is a thin plate bent such that end portions on one side are superposed with each other while an end portion on the other side secures a large gap therein so that sufficient venting can be secured. This laminated blade is held by a block, and this block is fitted in a recessed pocket in the tire molding surface of the mold, thereby forming a vent chamber surrounded by the pocket and the block. Air and gas are discharged into the vent chamber through a small gap between the one end portions of the laminated blade and the large gap in the other end portion. However, this vent mechanism requires: a step of forming the pocket in the tire molding surface of the mold after its casting; a step of making an assembly being the block holding the laminated blade; and a step of fitting this assembly into the pocket. Thus, the number of processing steps is increased, causing a problem of increased manufacturing time.
Patent Document 2 proposes multiple, separate shots of molten metal at the time of casting each piece that forms a mold. The cast piece has a small gap formed in the cast boundary between shots due to solidification shrinkage of the molten metal. This gap serves as a vent path. However, since this proposal requires multiple, separate shots of molten metal, the number of processing steps is increased, causing a problem of increased manufacturing time.